Bird Colonies About 13 percent of bird species, including most seabirds, nest in colonies. Colonial nesting evolves in response to a combination of two environmental conditions: (1) a shortage of nesting sites that are safe from predators and (2) abundant or unpredictable food that is distant from safe nest sites. First and foremost, individual birds are safer in colonies that are inaccessible to predators, as on small rocky islands. In addition, colonial birds detect predators more quickly than do small groups or pairs and can drive the predators from the vicinity of the nesting area. Because nests at the edges of breeding colonies are more vulnerable to predators than those in the centers, the preference for advantageous central sites promotes dense centralized packing of nests. The word “vicinity” in the passage is closest in meaning to •A.protection•B.region•C.population•D.resourcesThe yellow-rumped cacique, which nests in colonies in Amazonian Peru, demonstrates how colonial birds prevent predation. These tropical blackbirds defend their closed, pouchlike nests against predators in three ways. First, by nesting on islands and near wasp nests, caciques are safe from arboreal mammals such primates. Second, caciques mob predators (work together as a group to attack predators). The effectiveness of mobbing increases with group size, which increases with colony size. Third, caciques hide their nests from predators by mixing active nests with abandoned nests. Overall, nests in cluster on islands and near wasp nests suffer the least predation. Paragraph 2 implies which of the following about yellow-rumped caciques? •A.They are comparatively unlikely to be harmed by the wasps that attacktheir predators.•B.They are able to protect their nests without using colonies.•C.Mixing active nests with abandoned nests is the least useful way ofdefending their nests.•D.Most of their predators are members of other bird species.Paragraph 2 claims that yellow-rumped cacique colonies defend themselves from predators in all of the following ways EXCEPT: •A.They establish colonies in hart-to-reach places.•B.They physically attack invading predators.•C.They hide active nests among previously used ones.•D.They limit the size of their colonies so they are hard to findCoordinated social interactions tend to be weak when a colony is first forming, but true colonies provide extra benefits. [▇] Synchronized nesting, for example, produces a sudden abundance of eggs and chicks that exceeds the daily needs of local predators. [ ▇ ] Additionally, colonial neighbors can improve their foraging by watching others. [▇] This behavior is especially valuable when the off-site food supplies are restricted or variable in location, as are swarms of aerial insects harvested by swallows. [ ▇ ] The colonies of American cliff swallows, for example, serve as information centers ...
